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The federal government, known as the Supreme Power of the Federation, is constituted by the Powers of the Union: the legislative, the executive, and the judicial. Mexico City, as the capital of the federation is the Federal District, the seat of the powers of the Union. All branches of government are independent; no two separate branches must be vested upon a single person or institution, and the legislative power must not be vested upon a single individual.

The legislative power[1] is vested upon the Congress of the Union, a bicameral congress comprising the Senate (Spanish: Cámara de Senadores or Senado) and the Chamber of Deputies (Spanish: Cámara de Diputados). The powers of the Congress include the right to pass laws, impose taxes, declare war, approve the national budget, approve or reject treaties and conventions made with foreign countries, and ratify diplomatic appointments. The Senate addresses all matters concerning foreign policy, approves international agreements, and confirms presidential appointments.

The Chamber of Deputies is formed by 500 representatives of the nation. All deputies are elected in free universal elections every three years, in parallel voting: 300 deputies are elected in single-seat constituencies by first-past-the-post plurality (called uninominal deputies), and the remaining 200 are elected by the principle of proportional representation (called plurinominal deputies) with closed-party lists for which the country is divided into five constituencies or plurinominal circumscriptions. Deputies cannot be reelected for the next immediate term.

Being a supplementary system (PM) of parallel voting, proportionality is only confined to the plurinominal seats. However, to prevent a party to be overrepresented, several restrictions to the assignation of plurinominal seats are applied:

A party must obtain at least 2% of votes to be assigned a plurinominal seat;

No party can have more than 300 seats (uninominal and plurinominal together), even if the party gets more than 52% of the votes;

No party can have more deputies (uninominal and plurinominal) whose proportion in the Chamber is eight percentage points greater than the percentage of votes obtained in the elections;

Senate

The Senate consists of 128 representatives of the constituent states of the federation. All senators are elected in free universal elections every six years through a parallel voting system as well: 64 senators are elected by first-past-the-post plurality, two per state and two for the Federal District elected jointly; 32 senators are assigned through the principle of "first minority", that is, they are awarded to the first runner-up party for each constituent state and the Federal District; and 32 are elected by proportional representation with closed-party lists, for which the country forms a single constituency. Senators cannot be reelected for the next immediate term.

The judiciary[2] consists of The Supreme Court of Justice, composed of eleven judges or ministers appointed by the President with Congress approval, who interpret laws and judge cases of federal competency. Other institutions of the judiciary are the Electoral Tribunal, collegiate, unitary and district tribunals, and the Council of the Federal Judiciary. The ministers of the Supreme Court will serve for 15 years and cannot be appointed to serve more than once.

Mexico City does not belong to any state in particular, but to the federation, being the capital of the country and seat of the powers of the Union. As such, it is constituted as a Federal District, ultimately administered by the Powers of the Union.[3] Nonetheless, since the late 1990s certain autonomy and powers have been gradually devolved. The executive power is vested upon a head of government now elected by first-past-the-post plurality. The legislative power is vested upon a unicameral Legislative Assembly. The judicial power is exercised by the Supreme Tribunal of Justice and the Judiciary Council.

The Federal District is divided into delegaciones or boroughs. Though not fully equivalent to a municipality in that they do not have regulatory powers, they have gained limited autonomy in recent years, and the representatives to the head of government are now elected by the citizens as well.